1. Technical Field
The present disclosure relates generally to nuclear magnetic resonance (NMR) logging and, more specifically, to techniques for identifying and removing artifacts in multi-dimensional distribution functions.
2. Background Information
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the subject matter described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, not as admissions of prior art.
Logging tools have long been used in wellbores to make, for example, formation evaluation measurements to infer properties of the formations surrounding the borehole and the fluids in the formations. Common logging tools include electromagnetic tools, nuclear tools, acoustic tools, and NMR tools, though various other types of tools for evaluating formation properties are also available.
NMR logging tools are used to measure the properties of nuclear spins in the formation, such as the longitudinal (or spin-lattice) relaxation time (referred to as T1), transverse (or spin-spin) relaxation time (referred to as T2), and a diffusion coefficient (D). Knowledge of these NMR properties can help aid in the determination of basic formation properties such as permeability and porosity, as well as the fluid properties such as fluid type and viscosity. Multi-dimensional NMR techniques may provide quantitative fractions of different fluids (e.g., oil, water, gas) and a better understanding of the diffusion properties of these fluids in the surrounding formation, including the effects of geometry and restricted diffusion. Diffusion relaxation time (D-T2) measurements have also shown to reflect hydrocarbon fluid compositions by correlations with their chemistry. It has been observed that in the practical implementation of these NMR techniques in logging tools, unphysical fast diffusion artifacts in the multi-dimensional distribution functions (e.g., 2D D-T2 maps) may occur. These artifacts may make fluid typing and the determination of fluid dynamics more difficult.